| ( | 10 | + | x | ) | ( | 100 | − | 5 | x | ) | = | 1120 |
| Left side of the equation = | 10 | ( | 100 | − | 5 | x | ) | + | x | ( | 100 | − | 5 | x | ) |
| = | 10 | × | 100 | − | 10 | × | 5 | x | + | x | ( | 100 | − | 5 | x | ) |
| = | 1000 | − | 50 | x | + | x | ( | 100 | − | 5 | x | ) |
| = | 1000 | − | 50 | x | + | x | × | 100 | − | x | × | 5 | x |
| = | 1000 | + | 50 | x | − | x | × | 5 | x |
| 1000 | + | 50 | x | − | x | × | 5 | x | = | 1120 |